The present invention relates to a semiconductor apparatus and to a method for producing the same, and in particular to a semiconductor apparatus and method for producing the same for use in, for example, an amplifying static induction type transistor wherein a surface of a semiconductor chip having a thick film electrode is coated with a passivation film, the semiconductor chip being molded with a resin mold.
Generally, a semiconductor apparatus such as an electric power amplifying static induction type transistor (hereinafter referred to as a power SIT) uses a thick film electrode of a predetermined thickness on the upper surface of a semiconductor chip to increase the current capacity and improve the withstand voltage of the apparatus. In addition, to stabilize the characteristics of the apparatus, the surface of the semiconductor chip on which the thick film electrode is disposed is coated with a passivation film. Moreover, this semiconductor apparatus is molded with a resin mold and then encased so as to improve the mechanical strength of the entire apparatus.
The characteristics, standards, and so forth of all semiconductor apparatuses (including the above conventional semiconductor apparatus) produced in accordance with predetermined processing steps should be determined by conducting various tests established by, for example, JIS (the Japanese Industrial Standards). In particular, the above power SIT generates a large amount of heat because it dissipates a large amount of power. Therefore, a cyclic temperature test should be conducted to evaluate the durability of the apparatus against variations in temperature.
FIG. 1 shows conditions of a semiconductor chip of a conventional power SIT upon which a cyclic temperature test is conducted. FIG. 1A is a plan view showing the entire surface condition of the semiconductor chip. FIG. 1B is a plan view of a principal portion showing the surface condition of a corner of the semiconductor chip of FIG. 1A. FIG. 1C is a sectional view of the principal portion showing the inner condition of the corner of the semiconductor chip of FIG. 1A.
As shown in FIG. 1A, after a cyclic temperature test has been conducted on a conventional power SIT, on opening the SIT and observing the entire surface condition of the rectangular semiconductor chip 1 in the apparatus it is likely to be revealed that no macroscopic change has taken place on the surface. However, as shown in FIG. 1B, detailed observation of the surface condition of a corner of the semiconductor chip 1 (the portion marked with a circle X in the figure) reveals that a large number of cracks 10 are present on the passivation film 4 disposed between the gate electrode 2 and the EQR electrode 3 and disposed on the circumference of the EQR electrode 3. In addition, as shown in FIG. 1C, a sectional observation reveals that the cracks 10 completely penetrate the passivation film 4 and extend into the field oxide film 5 and the doped polysilicon film 6. Moreover, these cracks 10 occasionally penetrate the field oxide film 5 and the doped polysilicon film 6 and extend into the p-type gate region 7, the n+ type EQR region 8, and the field portion of the n- type epitaxial region 9.
This occurs when the gate electrode 2 and the EQR electrode 3, of the semiconductor apparatus which are disposed on the upper surface of the semiconductor chip 1, are formed of a thin film and the semiconductor chip 1 is then molded with a resin mold. In the cyclic temperature test, the resin mold repeatedly expands and shrinks in accordance with the variation in temperature. The resulting pressure is concentrated in the vicinity of the bottom circumferences of the gate electrode 2 and the EQR electrode 3 of the semiconductor chip 1, thus producing a large number of cracks 10. These cracks 10 remarkably affect the characteristics of the semiconductor apparatus. If the cracks extend into a major semiconductor region such as the field portion 9a of the n--type epitaxial region 9, the designed transistor characteristics cannot be accomplished. In addition, even if the cracks 10 are suppressed from extending into the semiconductor region, as long as the field oxide film 5 in the vicinity of the bottom circumference of the gate electrode 2 is damaged, the withstand voltage is inevitably degraded. Thus, the reliability of a power amplifying semiconductor apparatus in which a large amount of current flows, is seriously reduced.